Study of the thermal degradation of poly(furfuryl methacrylate) by thermogravimetry

The thermal degradation of poly(furfuryl methacrylate) (PFM) has been studied by means of dynamic thermogravimetric analysis (TGA) in the temperature range 100–600°C under nitrogen and oxygen atmospheres at various heating rates, and the apparent activation energy for the interval 230–340°C corresponding to the first degradation step was determined. Isothermal TGA at 250°C, 275°C and 300°C was carried out and the apparent activation energy values obtained were compared with those determined in dynamic experiments. The residues from isothermal degradation experiments were analysed by infrared spectroscopy and the results seem to indicate that in the thermal degradation of PFM the formation of cyclic structures of 2,4-dimethylglutaric anhydride occurs in the macromolecular chains, together with partial depolymerization of polymer segments, as well as intermolecular crosslinking through oxidation of the C---H bond in position 5 of some furfuryl rings.     

Detailed kinetic modeling of pyrolysis of tetrabromobisphenol A

The thermal degradation of 4,4′-isopropylidenebis(2,6-dibromophenol), commonly known as tetrabromobisphenol A (TBBA), was studied by means of a semi-detailed kinetic model. TBBA is a widely adopted flame retardant. It decomposes in a temperature range between 200 °C and 500 °C, forming gaseous mixtures of HBr and harmful compounds such as bromine-containing phenols, the precursors of brominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs). These thermochemical characteristics constitute a significant risk of environmental contamination right throughout TBBA's whole life cycle. A kinetic model based on about 60 components (real and lumped species and radicals) and about 900 reactions satisfactorily reproduces the main aspects of TBBA degradation and volatilization. The model was validated by comparison with several thermogravimetric analyses, both isothermal and dynamic at 10 °C/min. The vaporization of pure TBBA, the formation of hydrogen bromide and of carbonaceous residue were all correctly predicted in quantitative terms right across the entire temperature range. Compared to conventional one-step global apparent degradation models, the proposed model spans much larger operating ranges, especially in predicting the gas phase products distribution. The results are encouraging and confirm the validity of the detailed kinetic model.     

Isothermal kinetic analysis of the thermal decomposition of magnesium hydroxide using thermogravimetric data

In the present study, the kinetics of the thermal decomposition of magnesium hydroxide is investigated, using isothermal methods of kinetic analysis. For this purpose, experiments in thermogravimetric analyser were carried out in standard values of temperature (350°, 400°, 450° and 500°C) which resulted in weight loss percent as a function of time. The data were further modified to give fraction reacted ‘' versus time to be tested in various forms of ‘' functions. In order to determine the mechanism of the magnesium hydroxide decomposition and the form of the conversion function which governs the dehydroxylation of Mg(OH)₂, four different methods of isothermal kinetic analysis were used. Applying each of these methods to the data, it was concluded that the nucleation mechanism predominates the Mg(OH)₂, decomposition for all values of temperature tested; at 350°C the kinetic model which represents the experimental data is that of reaction at phase boundaries (random nucleation), F₁: ln(1−)=kt) while for the higher temperatures 400°, 450° and 500°C the kinetic equation of nucleation and development in two dimensions, A₂: [−ln (1−)]^1/2=kt was found to fit better the experimental results. The activation energy was evaluated applying two alternative methods; the Arrhenius plot, using maximum rates of reaction, from which the activation energy was evaluated to be 20.54 kcal/mol. An alternative method based on plots of ln t versus 1/T corresponding to the same value of ‘' gave values of 10.72, 13.82 and 16.31 kcal/mol for ‘' values of 0.25, 0.50 and 0.75, respectively.     

Thermogravimetric analysis and kinetics modeling of isothermal carbonization of olive wood in inert atmosphere

The kinetics of olive wood carbonization is investigated by means of isothermal thermogravimetric analysis method. Measurements were carried out in a thermobalance for different fixed temperatures between 498 and 648 K. A two-stage semi-global kinetic model consisting of four sequential steps was proposed to derive kinetic parameters. The olive wood is classified in three pseudo-components. For the first two, similar thermal degradation mechanisms take place in a single reaction step. For the third, the thermal degradation takes place in two consecutive steps. The isothermal conditions allow the kinetic constants (activation energy and pre-exponential factors) to be estimated by means of the analytical solution of the mass conservation equations. An overall good agreement was obtained with activation energy values available in the literature.     

Thermal stability of an explosive detonator

Mercuric 5-nitrotetrazole is a possible replacement for lead azide. The thermal decomposition peak maximum ranged from 185 to 270°C as the heating rate increased from 0.1 to 100°C min⁻¹. The activation energy and frequency factor for thermal decomposition were determined from dynamic and isothermal DSC and isothermal TG data; the average values were 38.8 kcal mol⁻¹ and 3.56×10¹⁴ s⁻¹. A half-life experiment confirmed the kinetic constants and indicated that the decomposition reaction was first order. The heat of explosion was determined by a pressure DSC test and found to be 2587 J g⁻¹. The linear coefficient of expansion was 37±2×10⁻⁶°C⁻¹ from −60 to 160°C and indicated secondary transitions near −10 and 90°C. The specific heat was 0.0003154T+0.1339 in the region −40–90°C. The critical temperature for a slab with a half-thickness of 0.035 cm was calculated to be 232 °C.     

Thermal analysis of Na2CO3 · H2O crystals

Monohydrated sodium carbonate crystals have been grown by slow evaporation of its aqueous solution maintained at 40 ± 1°C. The thermal dehydration of this crystal has been studied by dynamic and isothermal TG measurements. It is observed from dynamic TG that the single molecule of water of crystallization is lost in two steps of 0.3 mole and 0.7 mole at temperatures 426 ± 5 and 454 ± 5 K, respectively. From isothermal and dynamic TG measurements, the kinetic parameters E and Z are calculated using different known forms of the function F(). It is observed that consistency of E and Z values in isothermal and dynamic TG measurements for the two dehydration steps gives the correct function F() = −[log(1-)]^0.5. The activation energies for this function for the two dehydration steps are ≈6 and ≈9 kcal mole⁻¹, respectively.     

Mechanism and kinetics of the isothermal thermodegradation of ethylene-propylene-diene (EPDM) elastomers

The thermal degradation behavior of a range of ethylene-propylene-diene (EPDM) elastomers, covering the whole range of composition, has been examined under isothermal conditions between 410 and 440 °C using thermogravimetric analysis. The kinetic parameters of degradation for the polymers have been evaluated using different mathematical models based on different proposed mechanisms of degradation. The experimental data were fitted to the models using non-linear regression analysis technique based on Marquardt-Levenberg algorithm. It appears that the degradation of EPDMs follows the Avrami-Erofeev two-dimensional nucleation model or a random chain-scission mechanism. No observable trend was found between the ethylene content of EPDM and the activation energy of degradation.     

Kinetics of pyrolysis and combustion of pine needles and cones

A wide kinetic study has been carried out under different conditions in TG and TG–MS for each material, at different operating conditions. Runs were carried out at three different atmospheres: N₂, N₂:O₂ 4:1 and N₂:O₂ 9:1. In addition to the dynamic runs carried out at constant heating rate, other runs were performed in an isothermal regime (constant heating rate until the set temperature is reached and then the set temperature is maintained constant).In addition, a study of the thermal decomposition for both materials was also carried out in a dynamic run using TG–MS in order to observe the evolution of the major compounds and to discuss the information that could be obtained.From the overall analysis of the data, schemes of reactions and kinetic values were calculated by integration of the differential equations and minimizing the squared differences between the experimental and calculated values. It is important to emphasise that the same set of parameters is proposed for the runs for each material, and depends on neither the heating rate in dynamic runs nor whether the run is carried out in a dynamic or isothermal mode.     

Thermogravimetric study of flame-retarding properties on phosphorylated beech sawdust

Beech sawdust (S) and samples containing 1% of H₃PO₄ (SP), (NaPO₃)_n (PS), P₂O₅ (POS), NaOH/P₂O₅ (SPS), NaOH (SS) or Na₂CO₃ (CS) were analysed using dynamic and isothermal thermogravimetry (TG) in nitrogen and oxygen environments. According to the results of dynamic experiments in nitrogen, the thermal resistance at 275 °C decreased in the order: S > SS > CS > SP> SPS > PS > POS, while in oxygen the order was: S > POS > SPS=CS=PS > SP > SS. The difference in residues obtained in nitrogen in comparison to oxygen environment reaches its maximum at temperatures from 300 to 325 °C and according to the decreasing values the following order could be listed: SS (300 °C/27%) > SP (325 °C/25%) > CS (300 °C/24%) > S (325 °C/23%) > SPS (300 °C/19%) > PS (300 °C/11%) > POS (275 °C/4%). This indicates that with a decreasing difference in residues formed in oxidative and inert environments the flame-retardant effect of the sample is increasing. The calculated initial rate constants of residue formation and gasification and the corresponding activation energies of the processes in nitrogen and oxygen from the isothermal experiments gave smaller values of rate constants for SPS than for S. For the SPS sample in comparison with S the activation energy of residue formation in nitrogen decreased while the three remaining values increased. The E_r* of PS in the oxygen is the biggest from all studied samples under the conditions used, while SPS gave the biggest E_g* in the oxygen environment. The phosphorus could be washed out with water from SP and SPS, while it remained in PS and POS. These last two samples also have the best flame-retarding properties according to TG analysis.     

Step-wise and one-step vacuum pyrolysis of birch-derived biomass to monitor the evolution of phenols

One-step and stepwise laboratory batch vacuum pyrolysis of a mixture of birch bark (ca. 46%) and birch sapwood (ca. 54%) was carried out in the temperature range 25–550°C. The pyrolysis oil (defined as the total condensates, including water and organics) was analyzed by GC–MSD and the quantity of phenols (referred to monolignols in this paper) was determined as a function of temperature. The active zone of decomposition and the maximum recovery of phenols were found to be in the temperature range 275–350°C. Distribution of phenols, charcoal and water as a function of temperature was investigated. Stepwise and one-step pyrolysis yielded total phenols of 4.43 and 2.51 wt.% (anhydrous feed basis), respectively. The yields of pyrolysis oil (62.39 wt.%), wood charcoal (23.25 wt.%) and gas ( 14.36 wt.%) produced by both methods were approximately similar, on an anhydrous feed basis.     

Measurements and particle resolved modelling of the thermo- and fluid dynamics of a packed bed

The objective of this study is to investigate experimentally and numerically into heat-up, drying and pyrolysis of a packed bed consisting of large single particles. The novelty of the current approach is that the numerical model contrary to continuum mechanic approaches considers a packed bed as an ensemble of a finite number of particles, which may have different material properties or sizes. The heat-up, drying and pyrolysis process of each particle is described sufficiently accurate by a set of one-dimensional and transient differential conservation equations for mass and energy. Applying this model to all particles, including interactions between them, of a packed bed forms the entire backed bed process as a sum of individual particle processes. The arrangement of particles within a bed defines a void space between the particles. The flow through the void space of a packed bed is modelled as a flow through a porous media taking into account interaction between the solid and the gaseous phase by heat and mass transfer. Experiments for drying and pyrolysis of a packed bed were carried out for validation in a temperature range of T=120–530 °C. The temperatures and the mass loss due to drying and pyrolysis were recorded during the experiments. The measured mass loss of the packed bed due to drying were well predicted by the constant evaporation temperature model of the particles and thus, indicating, that the drying process is transport limited by heat transfer for large wood particles in a temperature range of T=120–530 °C. A comparison between experiments and predictions of pyrolysis yielded reasonable agreement for temperatures above T=300 °C. For temperatures of T≈200 °C the deviations were not acceptable. However, the results show, that a particle resolved approach is well suited to describe packed bed processes.     

Biosensor analysis for the kinetic study of polyphenols deterioration during the forced thermal oxidation of extra-virgin olive oil

The process of artificial rancidification of extra-virgin olive oil due to heating in an oxidizing atmosphere was studied by testing an actual kinetic model of the process and monitoring the thermal oxidative degradation of the polyphenols contained in it. To this end, a series of oxidative degradation experiments were carried out on extra-virgin olive oil samples under isothermal conditions at 98, 120, 140, 160, and 180 °C using a thermostatic silicon oil bath. The experimental procedure used in this study carefully followed the recommendations regarding the study of olive oil rancidification set out in the AOM procedure. The change in polyphenol concentration with time was monitored at selected temperatures using a tyrosinase biosensor operating in an organic phase (n-hexane). The activation energy for the polyphenol degradation process determined using the MacCallum method was found to be practically constant throughout most of the process.

Furthermore, the application of the so-called “model-fitting” method to this process enabled the specific constant rates to be determined at the above-mentioned selected temperatures. In addition, a confirmation of the activation energy value was obtained by the “model-fitting” method and the algorithm of the kinetic model equation best-fitting the experimental curve representing the whole process was checked.

Finally, further very interesting observations were made, for instance, the half-life concentration values of polyphenols at selected temperatures between 98 and 180 °C.     

Kinetics of isothermal thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends

The thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends of different compositions was investigated by means of isothermal thermogravimetry in flowing atmosphere of synthetic air at temperatures 240–270 °C. The main degradation processes are dehydrochlorination of PVC and CPE. For calculation of the apparent activation energy and apparent pre-exponential factor two kinetic methods were used: isoconversional method and Prout–Tompkins method. True compensation dependency between Arrhenius parameters, obtained using Prout–Tompkins model, was found. Calculated kinetic parameters of isothermal thermooxidative degradation are close to those from non-isothermal degradation and confirm the assumption of the main degradation process in PVC/CPE blends.     

Drying and pyrolysis of wood particles: experiments and simulation

The objective of this study is to develop a flexible and stable numerical method to predict the thermal decomposition of large wood particles due to drying and pyrolysis. At a later stage, this model is applied to each particle of a packed bed and thus, forms the entire packed bed process as a sum of individual particle processes. Therefore, this approach can deal with particles of different sizes, shapes and properties. A general formulation of the conservation equations allows the geometry of a fuel particle to be treated as a plate, cylinder or sphere. The various processes such as heat-up, drying and pyrolysis are described by a set of one-dimensional and transient conservation equations for mass and energy. This allows for simultaneous processes e.g. reactions in time and covers the entire range between transport-limited (shrinking core) and kinetically limited (reacting core) reaction regimes. The particles interact with a gas phase by heat and mass transfer taking into account the Stefan correction due to the gas outflow during conversion. Experiments carried out span a temperature range between T=300 and 900 °C for particle sizes varying between 8 and 17 mm. A comparison between measurements and predictions of drying models yielded satisfactory agreement only for the constant evaporation temperature model and thus, indicating, that the drying process is transport limited by heat transfer for large wood particles. Likewise, predicted results of pyrolysis for the above-mentioned range of temperatures and sizes agreed satisfactorily with measurements.     

Kinetic model of the decomposition of a PET fibre cloth in an inert and air environment

The kinetics of the global thermal decomposition of a PET fibre cloth have been studied in three different atmospheres with nitrogen, 20 and 10% oxygen, using thermogravimetric analysis (TGA) between room temperature and 1050 K. Three different heating rates were used at each atmosphere condition. Moreover, several isothermal experiments in nitrogen and 20% oxygen have been carried out. For the pyrolysis of an old PET fibre cloth, the kinetic model comprises three independent reactions. The combustion kinetic model considers that pyrolysis of two fractions of the initial material occurs regardless of the oxygen concentration and then a combustion of the forming char and the third fraction starts. One set of parameters can explain all the isothermal and dynamic experiments at the three different heating rates used.     

Transition metal binding properties of the redox-active 1,4,7,10,13,16-hexa(ferrocenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane and its electrochemical behaviour in a non-aqueous solvent

Solution studies to elucidate the coordination behaviour and the electrochemical response of the ferrocene-functionalized polyazamacrocycle 1,4,7,10,13,16-hexa(ferrocenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane (L¹) by potentiometric methods and electrochemical techniques have been carried out. Potentiometric methods in the presence of Cd²⁺, Hg²⁺, Pb²⁺ and Zn²⁺ were carried out in 1,4-dioxane/water (70:30 v/v, 25°C, 0.1 mol dm⁻³ KNO₃). Electrochemical studies were carried out in acetonitrile/dichloromethane (50:50 v/v, 25°C, 0.1 mol dm⁻³ TBAClO₄) in the presence of transition metal ions and anions.     

DSC examination of alloys

The formation and thermal dissolution of dispersed particles was studied in aluminium alloys. It was found that only high heating rates (80°C min⁻¹) could provide DSC curves characteristic of the phase structure of the samples. The kinetic evaluation of the DSC curves was carried out by least squares curve fitting. In this way reasonable kinetic parameters and reliable peak resolution could be obtained for the overlapping peaks.     

Phase-transition studies of 5O.5 and 9O.4

As part of our detailed comparative studies of groups of liquid-crystalline compounds that belong to a homologous series, we present phase-transition studies of the compounds N-(4-n-pentyloxybenzylidene)4'-n-pentylaniline (5O.5) and N-(4-n-nonyloxybenzylidene)4'-n-butylaniline (9O.4) using different experimental techniques. The compound 5O.5 is reported to exhibit a phase sequence N, S_A, S_C, S_B and S_G, while 90.4 shows the sequence S_A, S_F and S_G. The salient features of our work on 5O.5 are (i) a new smectic F phase is found in place of the reported smectic B phase, which is confirmed by both miscibility and X-ray studies; (ii) the formation of smectic-C-like short-range order in the nematic phase well above the S_A-N transition; and (iii) a large tilt-angle variation in the smectic C phase (0-23·5°C) in a small temperature range (4·1°C). The phase changes across the S_A-I transition, and for the first time across S_F-S_A transition, are carried out by volumetric studies. The detailed inferences of these are also presented.     

High temperature thermal properties of KH2PO4: Phase transitions and decompositions

Phase transitions and the thermal decomposition of KH₂PO₄ have been examined from room temperature to above 300°C by means of hot-stage microscopy, isothermal gravimetry and differential scanning calorimetry. Phase transitions at 198 and 242°C are confirmed, with corresponding enthalpy changes 4.2 and 2.3 kJ mole⁻¹, but no evidence has been found of a transition reported near 110°C. The thermodynamic and other evidence suggest a structural change at 198°C while the change at 242°C is less profound, perhaps involving only changes in the form of the hydrogen bonding. Thermal decomposition occurs in four stages, under conditions of free vapour escape, with the loss of one-quarter of a mole of water per formula unit of KH₂PO₄ in each stage. The products of each stage of decomposition are tentatively identified.     

Thermoanalytical study of activated carbon regeneration. II. 0-, m-, p-nitrophenol desorption

Partial adsorbate release (63, 50 and 53% for o-, m-, and p-derivatives, respectively) occurs when a commercial activated carbon loaded with each nitrophenol isomer is heated between 25 and 950°C in a dynamic N₂ atmosphere. After the endothermic process of water removal below 150°C, three definite steps are associated with adsorbate release. Evaluation of the related energies is presented.